The X220 is nowhere near an "absolutely perfect" design, it's way too wide. I still use one as my daily driver, but come on. The screen bezels are huge, the keyboard stretched to fill its wide footprint, and the power plug juts out the back where it gets stressed against the floor in any cross-legged, or other tilted back usage setting.
The X61s was far closer to an absolutely perfect design, it just needed less plastic in the chassis. Things started going downhill with the X201s in the transition to wide aspect ratio displays, and X220/X230 arrived at full retard on that trajectory.